The present invention relates generally to gravity chutes for conveying bulk materials. More particularly, the present invention concerns an extensible and retractable chute which is especially suitable for conveying friable, agglomerated or sized particulate materials or dusty materials. Granular bulk materials such as friable coal, sized-coke and dusty ores, cement and grains are usually loaded into holds of cargo ships by automatic-conveyor loaders. The material must be conveyed downwardly into these large cargo holds to a depth of fifty feet, for example. In loading friable or easily breakable bulk materials such as sized stoker coal for power plant boilers, it is not possible to drop the material from great heights since the critical particle sizes will be broken-up by the free-fall impact. Likewise, free-fall delivery of dusty materials into cargo holds also causes severe air pollution and explosion hazards which cannot be tolerated.
Thus, in order to minimize these breakage and dusting problems, it is desirable to convey such bulk materials under controlled flow conditions until the material reaches its destination in the cargo hold. When loading a cargo hold, it is also necessary to periodically raise the bottom end of the conveying device as the level of bulk material increases in the hold so as not to bury the conveying device. A prior telescoping ladder chute which attempts to meet these objectives is disclosed in U.S. Pat. No. 3,926,290 to Isojima et al. which is said to be suitable for ship loading applications. This device has met with limited success. The early patent to Curtis, U.S. Pat. No. 997,276, discloses a zigzag gravity chute which is said to minimize dust and breakage problems when conveying coal, grain and other substances. The chute sections of Curtis are not freely retractable, however, which limits its usefulness in loading cargo holds, for example, where the bulk material gradually fills the space occupied by the conveying chute necessitating the periodic raising of the chute. A further zigzag, stationary loading chute is disclosed in U.S. Pat. No. 2,502,341 to Queirolo. Several prior zigzag-type gravity chutes having retractable chute segments are taught in U.S. Pat. Nos. 4,161,243 and 1,583,833 to Grisnich and Howell, respectively. These prior devices are not suitable for use in conveying bulk cargo over great heights due to their inherent structural shortcomings. In Howell, for example, each chute segment bears the weight of all subjacent chutes which imposes a serious limitation on the overall height of the device.
The present invention solves many of the problems heretofore encountered in loading friable and dusty bulk materials into cargo holds and like storage spaces. The present invention provides a gravity chute conveyor which eliminates breakage and dusting problems and which is relatively light in weight and yet capable of conveying heavy cargo loads over great heights, on the order of fifty feet, for example. The present invention further provides a bulk material conveyor which is quickly and easily extended and retracted from a position above the cargo hold. In the retracted position, the conveyor of the invention assumes a folded or nested configuration of extremely compact dimension which provides for advantageous storage and easy transport from hold to hold. The present invention further provides a bulk conveyor having a novel, weight-supporting segmented suspension system which foldably nests with each of the chute segments as the conveyor is retracted. The instant invention further provides a bulk material conveyor having light weight chute segments with seamless high density plastic liners which greatly increases the life of the chute segments and minimizes maintenance thereof. Because they are open, the chute segments cannot become plugged with material, as common in the prior art, which allows for a more lightweight structural design.